mime: FormatMediaType doesn't allow to create Content-Disposition #9624
Description
On Go 1.4 (darwin), mime.FormatMediaType checks whether the first argument (aptly called mediatype) contains a forward slash, and returns an empty string if it doesn't. This doesn't allow to use this function to format a Content-Disposition header, because the values for such header are not proper media types (they are usually inline or attachment). Notice that the documentation of the reverse function mime.ParseMediaType explicitly says that it can be used to parse Content-Disposition headers, so it looks like this limitation should be lifted.